Pivoting or oscillating torsional hinged mirrors provide a very effective, yet inexpensive replacement for spinning polygon shaped mirrors used in printers and some displays. As will be appreciated by those skilled in the art, many of the torsional hinged mirrors are MEMS type mirrors etched from a silicon substrate by processes similar to that used in the manufacturing of semiconductor devices. Early versions of the torsional hinged mirrors for providing a raster type scan for printing and displays required speeds of about 3 KHz. Multilayer mirrors that operate in this speed range or slower could be manufactured with a drive/sensing magnet that was readily mounted or bonded to the back side of the hinge plate or layer. Further, the size and shape of the permanent magnet could readily be selected such that the moment of inertia of the magnet balanced the moment of inertia of the mirror layer. Balancing the mirror layer and the permanent magnet on either side of the hinge plate or layer results in the mass center of the mirror assembly lying on the pivoting axis of the mirror. However, as the demand for higher and higher oscillating speeds has resulted in smaller and smaller mirror assemblies, the corresponding requirement of smaller permanent magnets has resulted in problems in manufacturing magnets sufficiently reduced in size.
More specifically, presently available manufactured disc shaped permanent magnets have a minimum diameter of about 0.50 mm and a length or depth of about 0.20 mm. Although, these dimensions are very small, the moment of inertia of a magnet the size is still greater than the moment of inertia of the mirror layer of the smaller high speed mirrors. Therefore, when these small magnets are mounted to the back side of the hinge plate or layer, they are still too large such that the center of the mass moment of the assembled mirror device does not lie on the pivoting axis. This unbalanced assembly is unacceptable.
Therefore, a method of fabricating a small high speed mirror assembly with the mass moment center of the assembly located on the pivoting axis of the assembly would be advantageous.